NetSpot - NetSpot is a free app for wireless site surveys, Wi-Fi analysis, and troubleshooting
inSSIDer - inSSIDer Essential makes it easy to maintain small business WiFi.
Kismet - Kismet is an 802.11 layer2 wireless network detector, sniffer, and intrusion detection system.
Wifiner - WiFi Analyzer - WiFi Analyzer. See your WiFi signal on a visually comprehensive map and make sure you are getting the best of your network
Homedale - With Homedale you can search for Wi-Fi / WLAN Access Points and monitor their signal strength.
WiFi Warden - WiFi analyzer providing details like frequency, channel, modem manufacturer and more.